Prevector Quick Destruct #9505

pull JeremyRubin wants to merge 2 commits into bitcoin:master from JeremyRubin:prevector-quick-destruct changing 3 files +50 −6

JeremyRubin commented at 8:01 PM on January 10, 2017: contributor

This is a minor performance optimization of prevector. If the stored type is trivially destructible (such as unsigned char which is the main use of prevector), there is no need to call clear on the entries before freeing.

The call to clear seems to not get optimized out completely (likely because of the --_size; side-effect) with -O3.

std::is_trivially_copyable seems to enjoy full cross platform support.

On the included benchmark, I see about a 3% performance improvement.
theuni commented at 8:42 PM on January 10, 2017: member

any chance you get the same gain by specializing erase() with std::enable_if and std::is_trivially_destructible, simply reducing it down to a memset in the specialized case? That way we'd still get the zero'd mem, and it'd get sped up in several other places as well.
Add prevector destructor benchmark aaa02e7f24
Only call clear on prevector if it isn't trivially destructible and don't loop in clear 45a5aaf147
laanwj added the label Resource usage on Jan 11, 2017
JeremyRubin commented at 6:47 PM on January 11, 2017: contributor

@theuni I think that works -- may as well wrap both locations.
JeremyRubin force-pushed on Jan 11, 2017
kallewoof commented at 12:08 AM on March 1, 2017: member

utACK 45a5aaf
dcousens commented at 12:58 AM on March 1, 2017: contributor

light utACK 45a5aaf
laanwj commented at 9:43 AM on March 14, 2017: member

utACK 45a5aaf
laanwj merged this on Mar 14, 2017
laanwj closed this on Mar 14, 2017
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